Aluminum is a lightweight, silver-colored metal that can be formed into almost any shape. It can be rolled into thick plates for armored tanks or into thin foil for chewing gum wrappers. It may be drawn into wire or made into cans. Aluminum does not rust, and it resists wear from weather and chemicals. Aluminum is called aluminium in English-speaking countries outside the United States. Its atomic number is 13 and its atomic weight is 26.9815.
Pure aluminum, known as Al on the periodic scale, is soft and has little strength. For this reason, aluminum producers almost always blend it with small amounts of copper, magnesium, zinc, and other elements to form aluminum alloys. The added elements give aluminum strength and other properties that make it one of the most useful of all metals. In fact, the world uses more aluminum than any other metal except iron and steel.
The largest share of aluminum alloy production goes to the construction industry for use in such items as window frames, gutters, and the roofs and sides of buildings. Manufacturers of transportation equipment use huge amounts of aluminum in airplanes, automobiles, boats, railroad cars, and trucks. The packaging industry makes beverage cans, bottle caps, foil pouches, frozen food trays, and other items of aluminum. Aluminum is used in much electrical equipment, including light bulbs, power lines, and telephone wires. Thousands of other products also contain aluminum. These products include air conditioners, cookware, golf clubs, knitting needles, lawn furniture, license plates, paints, refrigerators, rocket fuel, toasters, and zippers.
Aluminum is the most plentiful metallic element in the earth?s crust and the third most common of all the elements, after oxygen and silicon. Aluminum makes up about eight percent of the earth?s crust. But unlike some other metals, such as gold and silver, aluminum never occurs free in nature. It is always chemically combined with other elements. People had no way of separating aluminum from these elements until the 1800?s. Scientists then developed processes for separating the elements and producing aluminum. These processes have been used to make aluminum ever since.
Only a small percentage of aluminum is used in pure form. It is made into such items as electrical conductors, jewelry, and decorative trim for appliances and cars.
Almost all aluminum is produced in alloy form with up to 15 percent of one or more other elements. The chief elements are copper, magnesium, manganese, silicon, tin, and zinc. Copper and magnesium increase the strength and hardness of aluminum. Magnesium also makes aluminum easier to weld. Manganese helps aluminum resist rust and also provides strength. Silicon lowers the melting point of aluminum and makes it easier to cast. Tin makes aluminum easier to shape with metalworking tools. Zinc, especially when combined with magnesium, gives added strength. Other elements may also be alloyed with aluminum for special purposes. These elements include bismuth, boron, cadmium, chromium, cobalt, iron, lead, lithium, nickel, sodium, titanium, vanadium, and zirconium.
Aluminum, with its alloys, has many valuable properties that make it an exceptionally useful metal. These properties include light weight, strength, corrosion resistance, electricity conduction, heat conduction, and light and heat reflection.
Aluminum is one of the lightest metals. It weighs about 170 pounds per cubic foot – about a third as much as steel. As a result, aluminum has replaced steel for many uses. For example, some parts of automobiles and trucks are now made of aluminum rather than steel because lighter vehicles use less fuel. Products packed in aluminum containers cost less to ship because the containers weigh less than those made of other metals.
Although pure aluminum is weak, certain aluminum alloys are as strong as steel. Such alloys are used in the bodies of airplanes and trucks, in guardrails along highways, and in other products that require great strength. Aluminum alloys lose some strength at high temperatures, but unlike many other metals, they get stronger at extremely low temperatures. Aluminum alloys are widely used in equipment for processing, transporting, and storing liquefied natural gas, which has a temperature of ?260 degrees Fahrenheit.
Some metals corrode if they are exposed to oxygen, water, or various chemicals. A chemical reaction occurs that causes the metals to rust or become discolored. When aluminum reacts with oxygen, however, the metal forms an invisible layer of a chemical compound called aluminum oxide. This layer protects aluminum from corrosion by oxygen, water, and many chemicals. It makes aluminum especially valuable for use outdoors, where the metal resists the effects of wind, rain, and pollution.
Aluminum and copper are the only common metals suitable for use as electrical conductors. Aluminum conducts electricity about 62 percent as well as copper, but aluminum weighs about a third as much. Aluminum wire can therefore carry the same amount of electric power as copper wire that weighs twice as much. In addition, aluminum is more ductile than copper, which means it can more easily be drawn into wires. Aluminum wire is used for nearly all high-voltage lines in the United States.
The first large commercial use of aluminum was is cookware. Aluminum cookware heats up quickly and evenly. Aluminum also cools quickly, which helps make it popular for such items as beverage cans and ice cube trays.
Aluminum reflects about eighty percent of the light that strikes it. This property has made the metal widely used in lighting fixtures. Aluminum also reflects heat well. Buildings with aluminum roofs reflect much of the sun?s heat and so stay cooler in hot weather. When fire fighters must walk through flames, they wear special suits coated with aluminum to reflect heat.
Aluminum is nonmagnetic, which makes it valuable for protecting electrical equipment from magnetic interference. Aluminum does not produce sparks when struck and can therefore be used near flammable or explosive materials. The metal is not poisonous, and so food can be safely wrapped in aluminum foil and cooked in aluminum pots. Almost any metal working process can shape aluminum. It can also be bolted, riveted, welded, and otherwise joined by most methods used for other metals. Finally, aluminum can be recycled.
Most minerals, rocks, and soils contain aluminum compounds, but aluminum can be made inexpensively only from bauxite. Bauxite is the name for any ore that has a large amount of aluminum hydroxide- a chemical combination of aluminum oxide and water. Aluminum oxide, also called alumina, is the compound from which aluminum is made.
Most bauxite consists of 30 to 60 percent alumina and 12 to 30 percent water. It also contains iron oxide, silica, and titanium oxide. The color of bauxite depends chiefly on how much iron oxide the ore contains. The more iron oxide it has, the darker the color. Bauxite may be white, cream, gray, pink, yellow, red, or brown. Most bauxite is as hard a s rock, but some is as soft as clay.
The richest deposits of bauxite lie in tropical and near-tropical regions. The leading bauxite-mining countries include Australia, Guinea, Jamaica, and Brazil. About 85 percent of the bauxite mined in the United States comes from Arkansas. The remainder comes chiefly from Alabama and Georgia. Canada has no bauxite deposits.
Most bauxite deposits lie near the surface of the earth and are mined by the open-pit method. In this process, bulldozers and other earthmoving machines first clear away the overburden- the soil, rocks, and trees that cover the deposits. Next, the ore is blasted loose by means of explosives. Huge power shovels then scoop up the bauxite, and trucks or railroad cars carry it to a processing plant.
At the processing plant, the bauxite is crushed and then washed to remove clay and dirt. Some of the water in the bauxite is removed by drying to ore in kilns. The bauxite is then ground into a powder and shipped to a refining plant, where it will be made into aluminum.
The word aluminum comes from the term alumen. Alumen is the Latin word for alum, a group of aluminum compounds that occur in nature and which ancient peoples used in dyeing textiles. In 1746, Johann Heinrich Pott, a Prussian chemist, prepared alumina from alum. Scientists believed that alumina was a chemical compound that consisted of oxygen and an unknown metal. The British chemist Sir Humphry Davy called this metal alumium and later changed the name to aluminum. In 1809, Davy formed an alloy of aluminum and iron by electrically melting alumina with iron.
In 1825, Hans Christian Oersted, a Danish chemist and physicist, produced the first aluminum. Oersted prepared aluminum chloride form alumina. He then heated the aluminum chloride with an alloy of potassium and mercury, and a small lump of aluminum formed in the alloy.
In 1827, Friedrich Wohler, a German chemist, produced aluminum in the form of a gray powder by heating aluminum chloride with potassium. In 1845, he produced particles large enough to be weighed. Wohler discovered that aluminum was lightweight, and he was the first scientist to describe many of the other properties of aluminum.
In 1854, Henri Etienne Sainte-Claire Deville, a French chemist, improved on Wohler?s method. Deville used sodium instead of potassium to break down aluminum chloride. This process produced larger quantities of aluminum. Commercial aluminum plants using Deville?s method soon opened in France. The price of aluminum dropped from $115 a pound in 1855 to $17 a pound in 1859. However, it was still too costly for widespread use.
The growth of the aluminum industry increased greatly following two important developments in the 1880?s. They were the invention of the Hall-Heroult process and of the Bayer process.
In 1886, two scientists – Charles Martin Hall of the United States and Paul L.T. Heroult of France – developed an inexpensive way to make aluminum. Neither man knew that the other was working on the problem. However, each thought of dissolving alumina in the mineral cryolite and separating aluminum from the mixture by electrolytic reduction. Today, the Hall-Heroult process is used to produce nearly all the world?s aluminum.
Aluminum production soared during World War I as the fighting nations increased output to help fill their military needs. During the 1920?s, the development of new aluminum alloys and of improved methods of turning aluminum into useful products continued to boost production. The Great Depression of the 1930?s cut world aluminum output almost in half. But the start of World War II brought tremendous expansion in production. In 1941, Reynolds Metals Company became the second producer of primary aluminum in the United States.
The demand for aluminum has grown steadily with the continuing development of new uses for the metal. Aluminum is used in solar-heating systems that absorb the sun?s rays to heat houses and other buildings. The production of aluminum by electrolytic reduction requires an enormous amount of electricity. To help conserve energy, the aluminum industry has stepped up efforts to recycle aluminum cans and other scrap. Remelting scrap to produce new aluminum takes less than 5 percent of the energy needed to make the metal from bauxite. Recycling also saves bauxite.
The world has enough bauxite to last from 200 to 300 years. About 75 percent of the deposits lie in countries that belong to the International Bauxite Association. This association was formed in 1974 to increase revenues from bauxite mining among the member countries. The IBA nations have established prices on ore they export and have raised taxes on bauxite mined in their countries by foreign firms.
Partly because of actions taken by the IBA, the U. S. aluminum industry is working to develop inexpensive methods for obtaining alumina from other materials. These materials include various clays; such ores as alunite, anorthosite, dawsonite, and nepheline syenite; and wastes from coal mining. Alunite and nepheline syenite have been used to reproduce alumina commercially in Russia.
Aluminum, one of the most common and most commercially produced metals, greatly affects the world we live in today. Without aluminum, we wouldn?t have many of the things we use everyday, like pop cans, cookware, or refrigerators. The world would not be able to function without aluminum do to its dependency on it for electrical and transportation equipment. It has revolutionized the automobile and plane industry, as well as made our lives easier with the simple foil we use for storing and cooking food. Overall, aluminum has influenced our lives greatly and continues to be a major contribution as we enter the new millenium.